1. Field of the Invention
The present invention relates to an electric car and, more particularly, to a power unit for the electric car.
2. Description of the Prior Art
In the prior art, there is known an electric car on which a motor is mounted as a drive source. FIGS. 10(a), 10(b), 10(c), 10(d) and 10(e) are diagrams showing examples of the structure of electric cars of the prior art. FIG. 10(a) shows an example in which two motors 63 and 64 are arranged in tandem to drive front or rear wheels. FIG. 10(b) shows an example in which two motors 65 and 66 are separately disposed to drive the front and rear wheels, respectively. FIG. 10(c) shows an example in which four separate motors 67, 68, 69 and 70 are used to drive the four wheels, respectively. Reference numerals 51 to 62 designate wheels; and numerals 71 to 73 designate differential gears. Moreover, the power unit for driving those motors is usually exemplified by a battery such as a lead battery or a generator and is mounted adjacent the rear wheels, as shown in FIG. 10(d) or adjacent the front wheels, as shown in FIG. 10(e). In FIGS. 10(d) and 10(e), numeral 74 designates a car body, and numerals 75 and 76 designate batteries.
However, the electric car of the prior art is accompanied by a problem that it cannot sufficiently cope with the various running conditions required of the vehicle where its motors are energized by the battery only, which is fixedly mounted thereon. Generally speaking, an electric car operates under various running conditions such as travel over a short distance, travel over a long distance, travel at a low speed, and travel at a high speed. A battery has a high power density so that it can produce a high current for a short time, but has a low energy density, i.e., a low energy output per unit volume. As a result, an electric car powered by a battery can only travel a short distance and is unable to satisfy all the various running conditions.